Aspergillus is a common fungus that is typically not a pathogen, but in immunosuppressed patients, such as those undergoing chemotherapy or stem cell/solid organ transplant, it can be a highly lethal disease with approximately 50% mortality, even with therapy. The disease is often first detected by a nodule in the lung on a computed tomography (CT) scan. Typically, a bronchoscope is placed into the lung and fluid is aspirated, which can make a diagnosis. Alternatively, a lung biopsy can be performed, by inserting a small needle into the lung and withdrawing lung tissue. Both procedures have significant morbidity/mortality and their yield is suboptimal. Noninvasive imaging can detect a nodule, but the nodule may be due to cancer, or other bacterial infections or unusual infections such as nocardia. Thus, a need exists for a noninvasive diagnostic test specific for fungal infections.